The present disclosure relates to semiconductor processing methods, and particularly to methods for anisotropically etching a nitrogen-containing dielectric layer at low energy, and structures for effecting the same.
“Trench-first” BEOL applications suffer issues due to residue formation with exposed metal surfaces, metallic hard-mask retention, and damage to low-k materials such as organosilicate glass throughout the pattern transfer process. Residual fluorine is usually linked to residue formation as well as low-k damage. However, residual fluorine is needed to provide sufficient etch rate for the material of a cap layer during the final stage of the pattern transfer process.
Increasing hard mask retention through process optimization is challenging. Thus, there is a lower limit on the initial thickness of the hard mask that can be employed for adequate lithography process window.
Deposition of removable sidewall polymer deposition to impede damage to the low-k materials has been extensively attempted. The removable sidewall polymer deposit fills the periphery of an opening formed during an anisotropic etch process. The removable sidewall polymer deposit is removed, by a wet etch or a dry etch, during subsequent etching processing steps once the bottom of the trench is reached at the end of the anisotropic etch process. The requirement for removal of the sidewall polymer deposition severely limits the etching process window for the anisotropic etch, and effective increases the minimum dimension of a via hole that can be formed by the anisotropic etch.
Thus, an anisotropic etch process is desired that does not fill a periphery of a via hole with a polymer and provide protection to the low-k materials at the same time.